Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

20 Understanding Veritas Volume Manager

How VxVM handles storage management

VxVM uses two types of objects to handle storage management: physical objects and

virtual objects.

■ Physical objects—physical disks or other hardware with block and raw operating

system device interfaces that are used to store data.

■ Virtual objects—When one or more physical disks are brought under the control of

VxVM, it creates virtual objects called volumes on those physical disks. Each volume

records and retrieves data from one or more physical disks. Volumes are accessed by

file systems, databases, or other applications in the same way that physical disks are

accessed. Volumes are also composed of other virtual objects (plexes and subdisks)

that are used in changing the volume configuration. Volumes and their virtual

components are called virtual objects or VxVM objects.

Physical objects—physical disks

A physical disk is the basic storage device (media) where the data is ultimately stored.

You can access the data on a physical disk by using a device name to locate the disk. The

physical disk device name varies with the computer system you use. Not all parameters

are used on all systems. Typical device names are of the form c#t#d#, where:

■ c# specifies the controller

■ t# specifies the target ID

■ d# specifies the disk

Figure 1-1 shows how a physical disk and device name (devname) are illustrated in this

document. For example, device name c0t0d0 is the entire hard disk connected to

controller number 0 in the system, with a target ID of 0, and physical disk number 0.

Figure 1-1 Physical disk example

VxVM writes identification information on physical disks under VxVM control (VM

disks). VxVM disks can be identified even after physical disk disconnection or system

outages. VxVM can then re-form disk groups and logical objects to provide failure

detection and to speed system recovery.

For HP-UX 11.x, all the disks are treated and accessed by VxVM as entire physical disks

using a device name such as c#t#d#.

devname